Keith Lane, P.E., RCDD/NTS Specialist, LC, LEED AP, Vice President, Engineering, SASCO, Seattle
Articles
Fused Distribution May Not Always Be Necessary
Editor's note: This month, we wrap up author Keith Lane's three-part series on the 2005 NEC and emergency power distribution system design, which has included discussions of how the updated code will affect switchgear and the potential repercussions of selective coordination. Visit the Electrical community of csemag.
The Skinny on Switchgear and the New NEC
It must be understood that the short time delay from not having an instantaneous trip can allow fault currents to flow for several cycles (typically up to 30 cycles), which can subject the electrical system to high mechanical and thermal stresses. The system equipment must also be coordinated to ensure it can withstand this tripping time delay. Switchboard construction will handle its rated fault current for only three cycles, while switchgear construction can handle its rated fault current for 30 cycles. There is, however, one particular manufacturer that I know of who makes a hybrid type of switchboard that will handle the rated fault current for 30 cycles.
New NEC Could Change Emergency Power Distribution System Design
The new 2005 National Electrical Code (NEC) has been out and in circulation and is close to being adopted in the Northwest. Based on conversations with local code officials in the Seattle area, it is my understanding that the 2002 NEC will no longer be utilized and the 2005 NEC will take effect around September. There are some changes brewing in the 2005 NEC that could significantly transform the way emergency distribution systems are designed and built in the near future, and I think it is important to look at these changes, as well as some new definitions. NEC 100 Definitions: Coordination (Selective) - Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings and settings. NEC 700.27: Coordination - Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. NEC 701.18: Coordination - Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. NEC 517.26: Application of Other Articles - The essential electrical system shall meet the requirements of Article 700, except as amended by Article 517. For clarity it is important to include the NEC definition (Section 100) of overcurrent and the fine print notes defining "Emergency Systems and Legally Required Standby Loads" in Sections 700 and 701 below: Overcurrent: Any current in excess of the rated current of the equipment or ampacity of the conductor.
Elevating Emergency Power Requirements for Elevators
There are many items in the International Building Code that are different from the Uniform Building Code and can affect the electrical distribution system in commercial buildings.
The Electrical Impact of IBC Fire Pump Criteria
With the recent implementation of the International Building Code in the state of Washington, a need to increase fire pump horsepower has arisen. But equally important is the need to increase the size of associated generator and standy power equipment. In recent design meetings with fire-protection engineers, it has been brought to our attention that the pump size calculations under the Uniform...